Field of the Invention
The present invention is related to a confocal microscope apparatus, a stitched image construction method and a computer-readable medium.
Description of the Related Art
Confocal microscope apparatuses have conventionally been known as apparatuses that measure the three-dimensional shape of an object in a contactless manner. Among such confocal microscope apparatuses, laser scanning confocal microscope apparatuses, which use a laser as the light source, such as one described in Japanese Patent No. 3847422 for example are currently known and adopted widely in industry.
A laser scanning confocal microscope apparatus irradiates the subject with a laser beam that is condensed by the objective into a spot, and thereby scans the subject in the two-dimensional directions (XY plane directions). Then, the light reflected from the subject is received by a detector via a confocal diaphragm. Because the opening of a confocal diaphragm is formed at a position that is optically conjugate with the focal position of the objective, only light reflected from a portion in focus passes through the confocal diaphragm so as to be received by the detector. This makes it possible for a laser scanning confocal microscope apparatus which has a focal depth that is shallower than that of normal optical microscopes to obtain a luminance image in which only a focal portion has been imaged. This type of image is generally referred to as a confocal image. Hereinafter, an image obtained by a device having a shallow focal depth is referred to as an image with a shallow focal depth.
When the surface shape of a subject is measured by using a laser scanning confocal microscope apparatus, the shallowness of a focal depth is utilized. Specifically, a plurality of confocal images with shallow focal depths are obtained while changing the relative distance between the objective and the subject in the optical axial directions (Z directions). Then, by obtaining the Z position (i.e., focal position) that results in the maximum luminance at each pixel position from a plurality of confocal images, the surface shape of the entire surface of the subject is measured. Also, by treating the maximum luminance value at each pixel position identified from a plurality of confocal images as a new luminance value of each pixel so as to construct a new image, an image in which all spots on the subject surface are in focus can be obtained. This image is referred to as an all-in-focus image or an extended-focus image. The image data of an all-in-focus image is used together with measurement data of a surface shape in various occasions. Note that the measurement data of a surface shape is also referred to as height measurement data.
As a general rule, in order to perform accurate measurement in the Z directions by using a confocal microscope apparatus, it is desirable that the measurement be performed in a setting with a shallow focal depth, i.e., in a setting with a high magnification for the objective. However, a high magnification reduces an area that can be measured at a time (which will be referred to as a measurement visual field area). Because of this, image stitching techniques are used for measuring a wide area with high accuracy in the Z directions. Note that, instead of the term “stitching”, terms such as “jointing”, “tying”, etc. are also used to represent similar meanings.
As an example of a measurement method using an image stitching technique, the method of Japanese Laid-open Patent Publication No. 2004-170572 is known. In this method, measurement is performed while moving a stage in the X and Y directions at an appropriate pitch so that part of a measurement visual field area overlaps part of another measurement visual field area that is adjacent to the measurement visual field area. Then, by jointing a plurality of images corresponding to the plurality of measurement visual field areas obtained in the measurement, a stitched image of an area wider than that of each of the measurement visual field areas is constructed, and thereby the height data of that wider area is obtained. This method makes it possible to measure an area in a desired size even when the microscope apparatus has a high observation magnification. Hereinafter, the entire area that is to be measured will be referred to as a measurement target area.